Your boyfriend may still be affected by the argument that you both had.
Even though he has since sent you a message apologizing, there may still be a part of him that is caught up in all that was said during that argument and what caused the argument in the first place.
He may be coming online and viewing what you are doing in social media but not saying a word because he still wants to feel connected to you in some capacity, but he isn’t entirely comfortable with communicating with you in these moments because of the lasting effect that the argument had on him.
He may have actually apologized to you prematurely.
In other words, there may be more about this argument that is bothering him.
If it has been 28 hours since he communicated with you, he may now be in the process of dissecting what that argument was really about.
Sometimes, guys in a relationship just need some time to process their emotions.
When they do, there is a chance that they will either proceed with the relationship as normal and let that incident go, or they may want to talk about it some more.
Try to avoid panicking.
Doing so could make you start messaging him in desperation and this could actually cause yet another argument or make him feel that much more uncomfortable.
Instead, let him reach out to you again.
When he does, ask him whether he would like to talk about what happened.
If he does, this would be an opportunity for the both of you to speak freely and give yourselves the opportunity to come to terms with whatever issues there are in the relationship and hopefully come up with solutions.
If he tells you that he doesn’t want to talk about it, then let him know that you are always open to talking about it if he ever chooses to.
This helps in giving him a degree of reassurance that you are open to listening to him if he ever wants to talk about that argument in greater detail.
Approaching your next interaction with him in this way may be what helps in making your relationship less strenuous at this time, thereby allowing the both of you to gradually get back to how it used to be.