who to choose??

I have been in an on / off again relationship with by boyfriend of 10 years. as of now we are on…for the last 4 years we have been together – bought a house about 3 years ago. We are both 29 years old. About 5 years ago we were not together and he had a child with a girl he was with for about a year. 9 months of it was the pregnancy. I have also been at my job for almost 8 years. there is a co worker of mine who is 35 and got laid off about 2 years ago and recently came back to my office. when we met – it was like an instant chemistry. FRIEND WISE! We clicked. He knew i had a man and what my situation was cause we always talked about everything. He has a 12 year old daughter too. but – when he got let go – we used to email each other to see what what was going on with each other to keep in touch. then he emailed me saying that he never had a connection with anyone like he did with me and he had a crush but since i had a man he backed off…well i kind of felt the same and i told him in the email as well. he is completely different than my bf and actually cares about my needs. Nothing has ever happened and i am kind of scared that if something did – i would leave the guy i have put so much work into. it is hard not to think about the co worker because he always appears in my dreams! and in my dreams nothing really happens – cuddling and laying together is about it. we have become closer since he has returned to my office and things have left off where they did before. i feel like i am in limbo with this. just getting this off of my chest – maybe it will help me not think of him so much.