Co-worker asked me out. I have a boyfriend and don’t know what to do

So as the title says my co-worker has asked me out on a date. I’ve had a crush on him for months but have brushed it off as harmless attraction never thinking he’d like me let alone ask me out.

I currently have a boyfriend we’ve been together for a couple of years. I met him at my old job which we’ve left now. If I’m being quite honest I don’tw see a long term future in our relationship. We have too many differences in what we want for the future and it would be unfair on him to deprive him of a future he wants. I’ve told him this and he says I’m sure you’ll change your mind. I won’t.

When my co-worker asked me out the interaction was very short and awkward. I was caught off guard and turned him down (not that I could’ve said yes at the time). I said I don’t know if I can date someone from work and he walked off. He’s a really sweet and sensitive guy so I genuinely feel terrible for him as it would’ve taken so much courage for him to ask me that.

I’ve been mulling over what happened and have asked to have a chat with him on Monday. I’m not sure what I’m going to say. I can see myself with him happy but again the issues lies that I’m currently seeing someone who i do love. He is amazing and infatuated with me but like I said earlier I don’t see our relationship being something that will extend into the far future.

There have been moments in the past in my current relationship where I have wanted to break up with him but feel bad for what I know it will do to him, scared that it will be a mistake and incredibly guilty.

If I was in a different situation I would’ve wanted to say yes in a heartbeat.

Now that this has happened I can’t stop thinking of the what ifs and if my current relationship is worth perusing any longer. I’m feeling guilty for both men. Guilty that I’m considering breaking my current partners heart and confused at what I do and don’t want and confused at my feelings.

I’m an emotional hurricane internally right now and have cried over the situation on multiple occasions.

Has anyone else experienced this? Does anyone have any advise to help the situation?

Any insight, opinions or advise will be very much appreciated.