When you are intense about something, you are giving it a lot more. It could be more efforts or concentration. Intensity is more on the extreme side. It could be good or bad depending on a situation.
If someone is deeply passionate about something, they will give it their all. They may put in intense efforts to make sure that it comes out perfectly. In such an instance, going all in with intensity works out well.
Sometimes intensity can become too much such that it's negatively affecting others. Like when there's too much paparazzi around celebrities, or too much expectations on someone when they have already given their all.
It could also be a relationship where one party is kind of obsessed with the other. They give more of themselves and their time to the relationship. Their feelings towards their partner are also extremely strong in a way that the other party feels suffocated.
If something becomes too intense, it may ruin things that were going good in the first place. Try to take a step back and slow the pace. Here are intense quotes that remind you when too much is just too much.