NJ. Tenants had a break-up. Main breadwinner moved out.

[Monica Horn]

New landlord here, due to inheriting my parents home.  So I'm pretty "green" in all of this.  Pls be kind.

Have a 1 yr lease (drawn up by realtor) that is set to end Nov 1st.  Unmarried male and female are on the lease, jointly.  Female is the higher earner, making more than twice the male.  Seemed like the perfect tenants.  They break-up one month ago. She moves out.   Female told me then (verbally), that she is fully aware of her "financial obligation to the lease and will make sure full amount is paid until lease is up".    Welp, that worked for the first month after she moved out.  Got separate checks from each for half the rent.   Apparently the breakup got more nasty or the female spoke to someone who changed her mind as to her "financial obligation to the lease".  Now she is refusing to pay her half.  I did receive half of the rent this month from the male tenant, on time.  But I'm not sure the male can afford the full rent with just his income.  He also has 2 kids from previous relationship.  

At midnight tonight,  the rent due June 1st will be 5 days late.   Lease states:  " Each tenant is individually responsible for the entire rental payment.  Any arrangement for contribution or payments between Tenants does not affect or bind the Landlord.  A charge of $50 will be assessed for each rental payment received after the 10th of the month in which it is due.  Each charge will be paid as Additional Rent with the monthly payment.  Time for monthly payment is material and of the essence which means that if the Tenant does not pay rent fully by the 20th of the month, the Tenant will be in breach of this contract and subjects to termination of the lease."[=-

I know it's early yet, but I'd like to know what my plan of action should be IF my suspicions are correct and the female is withholding her half of the rent in order to force me to start eviction against her former partner (the male).  She has an excellent financial record and a very good job so I feel that she has the most to lose if full rent continues to go unpaid, so I don't know why she would risk this (maybe as a means of getting back at him?) but, who knows?