Why you break up for no reason may be a complicated issue worthy of consulting a T, but the issue of not saying mean things is easily solvable without incurring the cost of T. Just be polite. Be polite towards everybody you encounter, whether you sleep with that person or just buy coffee from them - regardless. Politeness is priceless and extremely useful in life, and by practicing being polite with him you will kill many, many birds because your politeness would serve you well in the workplace, at school, and everywhere else.