How can I stop the feeling of hurt

Knowing that my relationship is over and he's going to meet someone else (I think he already has) it makes me feel sick, and my stomach drops everytime I think of it and I feel my blood go all hot. Its such a horrible feeling, one minute I'm fine and then I'm not. I'm coming to terms with the breakup but the thought of him with someone else really hurts so bad and puts me into a dark hole 😭