Am I Taking sexual rejection too harshly?

Alright, so my boyfriend and I have been together for almost 7 years. We are a monogamous couple who had just started discussing having an occasional threesome. (We've never had one)Our sex life is good but could be better. We are able to have open discussions about how we are feeling. I feel that I bring up the same issue and examples I'm talking about to him but he just doesn't seem to understand where I am coming from.He has noticed a change in me being not as interested in him and he asked why. I explained to him that I feel sexual frustrated at times. He is not one to want to plan for sex and likes the randomness of an encounter. Which, I can understand.So some examples I give to him that I feel I'm being rejected by him thus causing me to become less interested are the following. 1. I'll roll over and start to hold him and get a little frisky. He then always turns to me and says he's too hot(temperature wise) or he's too tired. Causing me not to want to get the same reaction again in the future I stop trying because his happens numerous times. 2. He will place my hand on his dick, and he is hard, but then when I start to do something he says "ok I'm good" when I just get started to do something and then he goes to sleep. How am I not suppose to take this as being rejected? I don't understand. This is why I stop trying to be intimate.What are other suggestions I can say to reword how I'm feeling to make him understand? Am I missing something?