Hi
It sounds like it could be a da-thing.
DA's come from a one--person-psykologi system, they can have a tendency to auto-regulate and it can be a stress relieve to move away, when they are getting voulnarble/stressed/when there's too much intimacy. The closer you become, the more your partner can need distance.
People that are dealing with avoidant attachment shut down their attachment system due to neglect or active rejection if it's related to parenting styles. This can also occur if they've only been related to when learning a task so that they become overdeveloped in the left brain with less access to emotional availability or responsiveness.
They also dissociate into parallel attention or activities that don't involve other people as a defense against their stress related to connection.
During sex, they can deactivate the attachment system.
You can check out how good he is with eye contact and heart to heart contact.
Avoidant partners often withdraw if they feel too vulnerable and leave their partner feeling disconnected and dissatisfied. Once committed some avidant partners can experience a lessening of their libido/sex drive. A once pretty sexually active partner can seem to lose interest sexually. They would be this way with anyone and it has to do with them coming from families where there was not a lot of physical closeness. When you have become "deep family" to them they can start to unconsciously revert back to the patterns of their childhood attachments, which probably did not include a lot of close physical contact. Of course you can continue to ask for physical contact but be patient with them and try to find ways of approaching that don't provoke a defensive response in your avoidant partner. Also be careful not to trigger a shame response when discussing this with your partner as they tend to feel ashamed and embarrassed about letting their partner down in this way.
He can also forget about you, beeing in his own little bubble. Or he can zone out while you are still in contact. He can want you in the same house, but not in the same room.
He properly dont know, why his doing it, so be gentle.
DAs can also have a tendency to "scubadive" ect.
Fa's can also get triggered by intimacy, but their reaction is often stronger - they can create drama, ex. pick a fight, suddenly jumping out of bed and rushing/running out of the bedroom or go into freeze/collapse.
They can shift between disabling and activating of the attatchment system
Some likes kinky sex, bondage / SM ect
and boundaries can be a problem
There can be power / powerlessness struggles. Because of the high activation in their nerveussystem, they sometimes need more extreme sex. They can be dessocicated.
In disorganized, the attachment style is mixed with the threat response due to a parent being afraid of their own children or afraid from their own unresolved trauma or doing scary things to a child as they're raising them. There is a lot more fear involved and of course also dissociation related to unresolved relational trauma. The attachment system and the survival defensive responses can be over coupled and causing somatic, emotional and physiological confusion when a person is trying to connect more intimately in a relationship
A fa girl I know had sush a strong reaction lying in bed with her secure boyfriend, that she had to go to the toilet and throw up/womit.
You can check this thread out and see if there's more you can regonise.
jebkinnisonforum.com/thread/1071/healing-avoidant-da-attatchmentstyle 
