Every time i do something with this girl i regret it immediately and depression washes over me

I'm sorry if this isn't the right subreddit it just seems the most fitting.

I(18M) have no idea what to do every time i talk to this girl and agree to do something a sudden wave of guilt and depression wash over me, although there doesn't seem to be a reason to feel that way, i feel like I'm only in the relationship because I'm afraid to be lonely. I don't know what to do, i don't want to hurt her, its just that ill feel good one moment about us, And the next moment i feel like, i want to breakdown and cry. I don't know what to do,

I want to know if anyone else has felt like this and if they have what is it, im starting to feel like i am problem and nothing will ever fix it.

If anyone has any more question ill answer them,