I'm sorry to hear this. It is painful when cycling is shared with an SO and cycling lives are intertwined.

First of all, try to design your training/regular ride routes to be different than the route what you and he rode often together. If possible.

First few rides will be difficult but choose non-rainy days initially or something to make ride better.

Make your ride(s) with a specific goal in mind..meaning stopping somewhere to get something or have a snack. (yes, I know you will be sitting alone. Then bring a book..)

Of course ride with a friend/group if possible.

Don't abandon your bike completely, but either shorten (and intensify) your bike rides or do completely different routes, etc. Above all, don't be so hard on yourself. Cycle where your heart takes you in the moment. Cycle in the moment, not in the past nor in the future.