I typically don’t have trouble with either my homemade or store-bought Baileys curdling in coffee. Generally speaking, only a high-acid ingredient (e.g. lemon or lime juice) can cause it to curdle. If your brew is especially acidic, I recommend mixing the espresso and steamed milk together before adding the liqueur — the additional fat from the milk will act as a stabilizer. HOWEVER, make sure to keep an eye on your bottle. It may be that the entire batch of Irish cream has passed its expiration date, causing it to curdle. If this is the case, you’ll sadly need to dump the batch and start with a fresh bottle.