ok, your description is very minimal and I dont have the time for too much back & forth so here is a demo of my "best guess" of what you want.

Demo Flow (use CTRL-I to import)
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In lacinia, tellus vitae laoreet ultrices, lectus ligula dictum dui, eget condimentum velit dui vitae ante. Nulla nonummy augue nec pede. Pellentesque ut nulla. Donec at libero. \n4.Pellentesque at nisl ac nisi fermentum viverra. Praesent odio. Phasellus tincidunt diam ut ipsum. Donec eget est.\n","output":"str","x":790,"y":200,"wires":[["f4653b15cc1447a9"]]},{"id":"3414e001a8e61ee9","type":"template","z":"50f66a9ef4a1b0b7","name":"The itsy bitsy spider","field":"payload","fieldType":"msg","format":"handlebars","syntax":"mustache","template":"The itsy bitsy spider climbed up the waterspout.\nDown came the rain and washed the spider out.\nOut came the sun and dried up all the rain\nAnd the itsy bitsy spider climbed up the spout again.","output":"str","x":820,"y":260,"wires":[["f4653b15cc1447a9"]]},{"id":"b42091bdc1bbdd9d","type":"inject","z":"50f66a9ef4a1b0b7","name":"Load The itsy bitsy spider","props":[{"p":"payload"},{"p":"topic","vt":"str"}],"repeat":"","crontab":"","once":false,"onceDelay":0.1,"topic":"The itsy bitsy spider","payload":"true","payloadType":"bool","x":685,"y":260,"wires":[["3414e001a8e61ee9"]],"l":false},{"id":"f4653b15cc1447a9","type":"function","z":"50f66a9ef4a1b0b7","name":"Load Song","func":"const cleanLines = []\nconst lines = msg.payload.split('\\n')\n\nlines.forEach(function(e) {\n const parts = /(\\d*)\\W*(.*)/.exec(e)\n let line = parts[2]\n if (typeof line === 'string') {\n line = line.trim()\n if (line && line.length > 0) {\n cleanLines.push(line)\n }\n }\n})\n\nconst song = {\n // internals\n name: msg.topic,\n _lines: [...cleanLines],\n _lineCount: cleanLines.length,\n _currentLineNo: 1,\n // functions\n nextLine() {\n this.currentLineNo = this.currentLineNo + 1\n return this.currentLineNo\n },\n prevLine () {\n this.currentLineNo = this.currentLineNo - 1\n return this.currentLineNo\n },\n // property getters / setters\n get lines() { return this._lines },\n get lineCount() { return this._lineCount },\n get currentLine() { return this.lines[this.currentLineNo - 1] },\n get currentLineNo() { return this._currentLineNo },\n set currentLineNo(num) {\n this._currentLineNo = num\n if (this._currentLineNo < 1) {\n this._currentLineNo = 1\n } \n if (this._currentLineNo > this.lineCount) {\n this._currentLineNo = this.lineCount\n }\n }\n}\n\nmsg.payload = song\nreturn msg;","outputs":1,"noerr":0,"initialize":"","finalize":"","libs":[],"x":1060,"y":220,"wires":[["9d58dd71ed19aced","ae2a8716ac296151"]]},{"id":"9d58dd71ed19aced","type":"change","z":"50f66a9ef4a1b0b7","name":"","rules":[{"t":"set","p":"activeSong","pt":"global","to":"payload","tot":"msg"}],"action":"","property":"","from":"","to":"","reg":false,"x":1280,"y":220,"wires":[["56e18301e2ce53f4"]]},{"id":"ae2a8716ac296151","type":"debug","z":"50f66a9ef4a1b0b7","name":"debug 175","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"false","statusVal":"","statusType":"auto","x":1250,"y":260,"wires":[]},{"id":"480a3e6e7a5d10b9","type":"ui_text","z":"50f66a9ef4a1b0b7","group":"6d262ebe1aa5cfbf","order":4,"width":"17","height":"1","name":"","label":"šµ","format":"{{msg.payload}}","layout":"row-left","className":"","x":1350,"y":480,"wires":[]},{"id":"45758b0b136ba300","type":"change","z":"50f66a9ef4a1b0b7","name":"get title","rules":[{"t":"set","p":"payload","pt":"msg","to":"activeSong.name","tot":"global"}],"action":"","property":"","from":"","to":"","reg":false,"x":1160,"y":400,"wires":[["b61d077b0e35d2b4"]]},{"id":"c28a4242c47c462a","type":"ui_button","z":"50f66a9ef4a1b0b7","name":"","group":"6d262ebe1aa5cfbf","order":7,"width":"9","height":"1","passthru":false,"label":"Prev","tooltip":"","color":"","bgcolor":"","className":"","icon":"","payload":"true","payloadType":"bool","topic":"topic","topicType":"msg","x":690,"y":440,"wires":[["8fad65c32276de1f"]]},{"id":"7964da1bfe44ae9c","type":"ui_button","z":"50f66a9ef4a1b0b7","name":"","group":"6d262ebe1aa5cfbf","order":8,"width":"9","height":"1","passthru":false,"label":"Next","tooltip":"","color":"","bgcolor":"","className":"","icon":"","payload":"true","payloadType":"bool","topic":"topic","topicType":"msg","x":690,"y":480,"wires":[["abed403cc2d53333"]]},{"id":"8fad65c32276de1f","type":"function","z":"50f66a9ef4a1b0b7","name":"set prev line","func":"const song = global.get('activeSong')\n\nif (!song || song.lineCount <= 0) {\n msg.payload = ''\n} else {\n song.prevLine()\n}\n\nreturn msg;","outputs":1,"noerr":0,"initialize":"","finalize":"","libs":[],"x":850,"y":440,"wires":[["56e18301e2ce53f4"]]},{"id":"abed403cc2d53333","type":"function","z":"50f66a9ef4a1b0b7","name":"set next line","func":"const song = global.get('activeSong')\n\nif (!song || song.lineCount <= 0) {\n msg.payload = ''\n} else {\n song.nextLine()\n}\n\nreturn msg;","outputs":1,"noerr":0,"initialize":"","finalize":"","libs":[],"x":850,"y":480,"wires":[["56e18301e2ce53f4"]]},{"id":"040f703aa59229bc","type":"ui_ui_control","z":"50f66a9ef4a1b0b7","name":"on connect","events":"all","x":850,"y":400,"wires":[["56e18301e2ce53f4"]]},{"id":"b61d077b0e35d2b4","type":"ui_text","z":"50f66a9ef4a1b0b7","group":"6d262ebe1aa5cfbf","order":1,"width":"18","height":"1","name":"","label":"š¼","format":"{{msg.payload}}","layout":"row-left","className":"","x":1350,"y":400,"wires":[]},{"id":"c7d9d2405a47bd63","type":"change","z":"50f66a9ef4a1b0b7","name":"get current line","rules":[{"t":"set","p":"payload","pt":"msg","to":"activeSong.currentLine","tot":"global"}],"action":"","property":"","from":"","to":"","reg":false,"x":1180,"y":480,"wires":[["480a3e6e7a5d10b9"]]},{"id":"c504fad963af4719","type":"ui_text","z":"50f66a9ef4a1b0b7","group":"6d262ebe1aa5cfbf","order":3,"width":"1","height":"1","name":"","label":"#ļøā£","format":"{{msg.payload}}","layout":"row-left","className":"","x":1350,"y":440,"wires":[]},{"id":"93bb21e8a19d50f5","type":"change","z":"50f66a9ef4a1b0b7","name":"get line number","rules":[{"t":"set","p":"payload","pt":"msg","to":"activeSong.currentLineNo","tot":"global"}],"action":"","property":"","from":"","to":"","reg":false,"x":1180,"y":440,"wires":[["c504fad963af4719"]]},{"id":"56e18301e2ce53f4","type":"junction","z":"50f66a9ef4a1b0b7","x":1020,"y":460,"wires":[["45758b0b136ba300","c7d9d2405a47bd63","93bb21e8a19d50f5"]]},{"id":"6d262ebe1aa5cfbf","type":"ui_group","name":"Default","tab":"34f5e165d494f88b","order":1,"disp":false,"width":"18","collapse":false,"className":""},{"id":"34f5e165d494f88b","type":"ui_tab","name":"Home","icon":"dashboard","disabled":false,"hidden":false}]