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

This guy is one of her old co-workers that she started running with a few months ago. I am not a runner and this is something I often feel like she resents about me. Im happy to do physical things with her, but running isnt one of them. She claims he began to like her and wanted her to end things with me. She says she denied him and that's why he is sabotaging our relationship. Who do I trust? I want to believe her so bad. I had a gut feeling back in October when they first started hangin out.

He messaged me a few days ago and said once he figured out she lied about breaking up with me, he said no more. He said if he were being cheated on, hed want to know.

Cheating was always the worst outcome for me. I always said if you get that urge to stray, call me up and dump me now. Please love me enough to not lie. I am so hurt and angry that she put herself and our relationship in this position. I know our age gap is a concern but we always just complimented each other very well. We havent broke up yet but we have been taking some time apart. I know im all over the place and will never know the truth. I just want to hear from people in similar situations where you need to decide to trust a stranger who has a reason to perhaps sabotage a relationship or the girl youve been in love with for a year+ even though you have had a bad feeling about her faithfulness. There are a lot more details but I just need some support. I would do anything for this girl. But is loving her through this too much to ask? It might be.

Fuck me, this sucks. It feels like my entire chest cavity has been hollowed out. I want to cry but I am so livid I can not justify it.
<bot>: I suspected my GF of cheating and then got a confession from the guy via FB message. She denies it. Can't trust anyone.