Because you want to make this special for the BF, I'd cancel even though the health risk may not be bigger in BKK than the US.
BUT I'm currently traveling in Asia and flights to Asia are a mess. LH Group (incl. SWISS) is cancelling about 50% of their flights, so your carefully planned itinerary may fall apart before you get to BKK - and using UA miles makes it more difficult ... Even though you'll get there, it might not be together or your bf might get stuck on his own for a day or so in Zurich...
And flight restrictions are getting more complicated, with countries banning different countries of flight origin every day... Vietnam just cancelled visa-free travel from several EU countries, Qatar banned Asian countries, nobody knows what's next...
As an experienced traveler, you can work it out. A First-Timer might be frazzled...
Hopefully, the situation will be better by summer and the hysteria over, so you can show your BF the true Bangkok, not the masked one with fewer smiles...