A man shaking during receiving oral sex but can't ejaculate? stress or too tired?

So I am seeing this man who I have been very interested in and we have mutual feelings for each other.

It's great and we adore each others company.  We went back to his place and did loads of kissing (it was around 4am)  We probably went on for an hour cuddling and just talking.   Later things got a little steamed up when I asked him to touch my chest and he got really stiff.  So I thought I'll help him out down there,  and he was aware it was my first time giving oral sex to man because I just never did it.  He was moaning a lot, and was panting like mad and started bucking his hips but I noticed his legs were shaking A LOT.  After a while he told me that he won't be able to come because he felt like it was his first time all over again but apparently i was the best he's ever had and said my technique was great...  If it was so great,  why did he not ejaculate at all?  Is it possible he was too tired and stressed?  He did tell me he started feeling bad because he felt like he was abusing me since I literally gave him head for 45 minutes.

I really adored giving him oral sex and especially seeing his reactions was the most pleasurable thing for me.  But I would like help here to know whats going on... Help