"To love is to leave sometimes."
Translation:Sevmek gitmektir bazen.
discussion here may be of help: https://www.quora.com/What-is-the-word-order-in-Turkish especially Simge Topaloğlu's informative answer.
Not a native here, but -tir (as well as -dir -tır -dır) can somewhat be considered an emphatic article. Some books and resources on Turkish would make it equivalent to (is) in English. When I do exercises here I don't usually put it and in most cases it is considered correct. If the answer is wrong, then it might probably be that the contributors didn't include such answer even if it's correct sometimes (just sometimes). In official statements or signs ..etc you would find it used often to add emphatic sense and bring attention. This is how I understand it.