but作为一个连接词，自然可以把两部分都分开，如果分开两句话，看看“He lives alone.He doesn't feel lonely.” 不要在意那些所谓的固定搭配but+动词原型，你看看有but，两句话再合成一句话省略主语he是一样的
but后面的动词分为三种形式：
(1)but前面有实义动词do或其他形式时，后面的动词不定式不带to否则，带to。例：
I can do anything but sing.我就是不会唱歌。
I have no choice but to move.除了搬家，我别无选择。
She wanted nothing but to stay with him. 她只是想和他呆在一起。
(2)在nothing to do之后，动词不定式带不带to均可。例：
I have nothing to do but (to) wait. 我只好等着，没有别的方法。
There was nothing to do but (to) remain.只能留下来。
(3)在cannot choose but， cannot help but， cannot but后，动词不定式不带to。例：She could not choose but leave her children at home.她只好把孩子留在家里。
She could not but choose to leave her children at home.她忍不住把孩子们留在家里。
