两个to不是一回事，一个是动词不定式符号，一个是介词，所以就不一样了。至于什么情况下to是介词，你要积累相关短语动词（举例如下），动词不定式的用法就更多了，看看非谓语动词的语法应该就清楚了。
1.look forward to 盼望；期待(通常以愉快的心情）
We’re looking forward to seeing you very soon. 我们盼望很快再见到你。
2.be /become used to 习惯于；适应于
I’m not used to being spoken to in that rude way. 我不习惯于别人对我那样粗鲁地讲话。
注意used to do与be / become used to doing的区别。前者指过去经常的习惯(indicating a constant or frequent practice in the past)，后面接原形动词构成不定式形式，后者指现在的习惯，接动名词构成介词短语。此外，当be used 表示被动语态时，意思是“被使用，被用来”，后面应该接不定式。如：
Wood is often used to make paper. 木材常被用来造纸。
3.be / become accustomed to习惯于
The boy has become accustomed to speaking English in public. 那孩子已经习惯于在公众面前说英语了。
4.object to不赞成；反对
I object to being treated like an outsider. 我反对被当作局外人看待。
5.be opposed to 反对；反抗(某人或某事)
I amvery much opposed to your going abroad. 我非常反对你出国。
6. be addicted to doing 沉溺于；嗜好
He is addicted to drinking / smoking / lying. 他嗜好喝酒/抽烟/说谎。
7. devote oneself / sth. to 奉献(自己、时间、精力等)；致力于；专心；专门；献身
He devoted himself to promoting (the promotion of) world peace. 他一生致力于促进世界和平。
8. dedicate oneself / sth. to 奉献； 贡献(时间、精力等以从事崇高的事业或目的)
The doctor dedicated himself to finding a cure for the disease. 这位医生致力于寻找这种疾病的治疗法。
9. contribute to 有助于；促成
His pride contributed much to his cheating on the exam. 他的虚荣心在很大程度上驱使他考试作弊。
10. subject oneself / sth. to 使遭受；使经历;使蒙受；使有……之险
You shouldn’t have subjected yourself / your friends to being criticized like that. 你不应该使自己/你的朋友遭受那样的批评。
11. adapt oneself to 使适应；使配合
He is quick to adapt (himself) to living on his own. 他很快适应了独自生活。
12. adjusted oneself / sth.to 调整；调节;使适用；使便于使用
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