<human>: Can you summarize the given text in a few sentences?

For the past few months things between my girlfriend and I have become strained, it is arguably due to the result of another girl a meet at work, we'll call her M. M is a decently cool person to be around and is all around fun, but when it comes down to it we have very little in common. Heres where the story starts to get tricky, one night at a party both M and I got drunk and we made out, ever since that day I have felt terrible and every time I'm around my girlfriend I cant help but feel guilty.

my girlfriend and I share so many common interests, and we generally agree about everything, and for the year or so we have dated we havn't had a major fight or disagreement. Yet, ever since this event she has noticed both of us have become distant, which is my fault, and up to recently I haven't been able to say I love you to my girlfriend, and now even or sex has been somewhat.. off, and most of the time it just ends up with me not being able to finish and we just lay there.

I'm in a terribly difficult situation. The girl I care most about in the world and I have fucked it up and feel incredibly guilty about, while I have to deal with my co-worker, whom I have mixed feelings for, I'm not denying it. I don't know what to do, and I frankly need help from you, Reddit.
<bot>: Girlfriend[18] and I[18] of 1 year have become distant because I feel incredibly guilty about drunkingly making out with another girl, whom I may have feelings for