I had a similar experience and visited the US for months at a time to see my spouse. I was questioned by CBP officers why I had stayed so long in the past.
The biggest one, the max three months ESTA allowance for Thanksgiving and Christmas, was mainly on account of myself and my husband receiving a no-fault eviction notice and losing our flat in the UK after 4.5 years there. We did nothing wrong: landlady wanted to sell so we got kicked out. Simple as that. Lovely UK government does nothing to protect honest tenants.
With no room at my parents for both of us and too little time to find somewhere new given minimum notice, and with us awaiting a visa interview appointment to boot with no possible way of knowing when it would be, we had to split ways. Stressful isn't the word.
Of course, this was too long-winded to explain. I got the second degree until I told the CBP that I had an interview scheduled with the embassy for a visa - at this point it had processed through. They didn't let up until I showed them the confirmation letter/email. Nearly made me miss my connecting flight.
Be as honest as possible: bring payslips, car payment statements, anything that shows ties to your home country. Just incase. Expect scrutiny, and for them to ask the purpose of your stay and why you're visiting so frequently.
Honesty is the best policy.