You have a lot going on. You have a lot of stressors and life changes (say you identified that he was the breadwinner when you met and now you are both financially independent). You get up at different times. He does not see you in the evening. You are not eating breakfast together. You are tired. The routine is well organized, but grueling nonetheless. Yes, you are basically co-parenting. The distribution of household chores is inequitable: you get up earlier than he does, and yet in the evening you run around picking things up and packing lunches etc. for next morning while he is on the couch watching TV.

So the above is fully sufficient to explain lackluster love life.

It is impossible to say whether the one incident of infidelity has contributed to the lackluster love life or not. You will never be able to answer that question. Let me explain:

Let A, and B be possible stressors or triggers. Let X be a negative outcome. If A is sufficient to trigger X and A and B happened together and X ensued, we cannot say anything about the contribution of B or lack thereof. To test whether B by itself would trigger X, you would need to eliminate A and let B happen and observe what would follow.

You cannot set up this experiment in reality - that is self-evident. So truly, you will never be able to determine if the infidelity caused lackluster love life. This question cannot be answered with confidence. But you can run through the following hypothetical scenario in your mind to simulate the experiment that you cannot set up in reality:

Imagine that you are 23. And he is with you and cannot take his hands off you. You do not have a child yet and he is building houses successfully. Then something bad happens in his business and he starts losing clients. He is upset and demotivated, if not demoralized. In that low state, he happens to be in a bar with a woman and the incident happens. Then in 3 days you find out and he drops all contact with that woman. One year after the incident, he is back in business having many clients. How is your love life one year after that incident, when you are 24 and still not a career woman with a child? Think through it - reflect back on how you and he lived when you were 24 and try to picture what would have happened had that incident happened when you were 23.

I think this is the closest approximation you can get; the closest you can come to figuring out the cause and effect of various factors.