Hello here's what came to me.

Sexually dreams usually have nothing to do with sex..instead it is a way of us being repressed and not fully exerting ourselves as we should.We all feel free when were in that moment. In the first part, "in this dream he's giving me oral sex and somehow I accidentally suffocate him (he's all heat up because he reckons it's murder which I think is a completely different kettle of fish)"
you are more than likely desiring a person to be more forthright, to be more open to whatever situation you have. You might be yearning for this to happened, this have repressed you/blocked you from fully coming to. Our emotions our tied into so much, we have to separate the two to have clarity at all times with proper understanding

I've got a dead body on my hands which I have to hide behind a bush in a garden
Death is not bad at all, it is a turning point. And in this point, your dream is telling you there is a transformation in the process or will be. Don't try to force it or not allow it. Trust that you will have the strength and confidence to over come this. This relationship is coming at a point of put up or let it go. 
I think it's my garden but I can't tell.
Your decision. Its not going to be easy but have faith.

 I spend the rest of the dream shocked and distressed trying to avoid the police who I know won't believe that it was an accident and would lock me up. I remember cleaning a wooden clock (I'd seen it in the film memento the night before) and having to rub my fingerprints off surfaces. 
This could mean that you know what you have to do but you are going against it. This is a threat to you and you are being cautioned. This might cause you to be on a path of uncertainly, confusion, and sadness don't worry. Trust you intuition, it will never lie to you, either it will be revealed one way or another...You are doing the right thing or will do the right thing one way or another.

I had another dream that night in which my boyfriend was alive and I went to meet him with an old typewriter of his I'd fixed but when I showed him he said he didn't want it and walked off. I don't know if two dreams in the same night are connected...
You have to remember that you cant change people who don't want to be changed. I'm sorry, but this could signify the end of a relationship and the beginning of a new one. Don't feel bad, as I said nothing just happens and we all are walking our Divine paths. You take yours and they will take theirs, just know we are all looked after, and it will be OK. Once this does end, you will have acquired something and you will understand...Look at this from a different perspective once done, a positive not negative. Overall no worries, you are going be OK 

Anyway that's what I felt about it. peace, love and blessings - Dena